Conclusion

The anatomical evidence from humans is still insufficient. Nevertheless a picture of interlocked systems have started to emerge that support human memory function. The following account from Eichenbaum summarizes the current state of this picture:

When a relevant stimulus gains one's attention, the hippocampal rhythm is generated. The cellular mechanisms reflected in this rhythm effectively time-lock the arrival of multiple channels of exteroceptive sensory input with behaviorally generated events whose various functional representations in associational cortices converge on the hippocampal network. The overlapping inputs to hippocampal cells within the competitive networks of the hippocampal circuitry shape the configurations of events encoded by individual units, and distribute the representation across these units. The plastic properties of hippocampal physiology, primed by the synchronization reflected in the rhythm, support altered excitability states in cells maximally activated by these events. These cellular changes occur very rapidly, and immediately support a memory at sufficient strength to permit later reoccurrences of even a partial pattern of these events to reactivate the entire network. Furthermore, to the extent that new events share features with items stored previously, these representations are also reactivated and their activity interacts with the representation and storage of current events. Out of the interactions of current and stored representations in the hippocampal network emerges a ``memory space,'' encoding and updating representations of significant relations among new items and all other related items still excitable by hippocampal activity. Such instantiations and reinstantiations occur repetitively over a period of time, reexciting and possibly modifying long-term neocortical representations, enabling memory consolidation. Furthermore, such relational processing permits the same representations to be activated in different (including entirely novel) contexts. The manipulation of information as a consequence of the activation of this flexible representation may indeed constitute the neurobiological embodiment of conscious recollection; certainly flexible representations are required to support conscious recollection and awareness of previous experiences. While the precise processes underlying these putative steps in hippocampal processing and their linkage remain to be demonstrated, and indeed many other questions concerning the functional role of the hippocampus remain to be answered, the details of hippocampal memory processing and hippocampal-dependent memory representation are becoming ever more clear.